QTscore = [(SNP1 allele copy number)*(SNP1 effect estimate in ms)] + [(SNP2 allele copy number)*(SNP2 allele effect estimate in ms)] + … [(SNP68 allele copy number)*(SNP68 allele effect estimate in ms)] From the genotype score, we will determine the set of individuals who belong to the top or bottom quintile of QT genotype risk score (of whom, we expect 75% (n=133 per quintile)) to be eligible for our moxifloxacin study, based on our prior pilot work. We will invite these individuals to come in for a screening visit (see above) for the moxifloxacin study with a target enrollment of 40 in each genotype group.